1. Field of the Invention
The present invention relates to an internal combustion engine, and more particularly to an internal combustion engine including a port injection valve injecting a fuel into an intake port and an in-cylinder injection valve injecting a fuel into a combustion chamber.
2. Description of the Background Art
An internal combustion engine including a port injection valve injecting a fuel into an intake port and an in-cylinder injection valve injecting a fuel into a combustion chamber, in which the fuel is injected from the port injection valve and the in-cylinder injection valve at an injection ratio determined in accordance with an operation condition, that is, a double injection type internal combustion engine, has been developed. For example, Japanese Patent Laying-Open No. 2001-20837 discloses such an internal combustion engine.
In present days, when an internal combustion engine is used for a vehicle, in many cases, an air-fuel ratio sensor is provided in an exhaust pipe and a fuel injection quantity is subjected to feedback correction such that an air-fuel ratio is set to a prescribed value based on an output of the air-fuel ratio sensor. Here, it is the air-fuel ratio of exhaust gas generated as a result of combustion of the fuel in the combustion chamber that the air-fuel ratio sensor detects.
When two fuel injection valves inject the fuel, the air-fuel ratio as described above represents the air-fuel ratio of exhaust gas which is a mixture of exhaust gas generated as a result of combustion of the fuel injected from the port injection valve and exhaust gas generated as a result of combustion of the fuel injected from the in-cylinder injection valve. Therefore, a feedback correction amount calculated based on this air-fuel ratio is the sum of a correction amount for the fuel injected from the port injection valve and a correction amount for the fuel injected from the in-cylinder injection valve.
As such, in order to subject both fuel injection valves to feedback correction, an appropriate feedback correction amount for each fuel injection valve should be set. Otherwise, combustion fluctuation occurs, and a driver may feel uncomfortable or unpleasant.
According to the apparatus disclosed in Japanese Patent Laying-Open No. 2001-20837, however, feedback correction of the fuel injection quantity is neither mentioned nor disclosed.
In addition, though an apparatus according to Japanese Patent Laying-Open No. 2-153241 has two fuel injection valves, it is one fuel injection valve that is subjected to feedback correction. That is, this publication does not disclose a ratio between feedback correction amounts for the two injection valves.